"Inspired by true events" may be the best thing to happen to horror movies since the invention of the chain saw. By robbing audiences of their scary-movie mantra ("It's just a movie, it's just a movie"), a coy claim of realism can elevate middling suspense to abject terror ("If it happened once, what's to keep it from happening to me?").

Ironically, "The Strangers" doesn't need this kind of help: First-time writer-director Bryan Bertino's taut, spare thriller is plenty scary without relying on pseudo-historical context. Anchored by convincing performances from Scott Speedman and Liv Tyler, both of whom elevate their roles above the standard horror-movie caricature, this is an enormously unsettling movie.

From the opening scenes, Bertino simultaneously embraces and upends horror conventions: Even as they drive along a foggy, deserted road lined with pine trees, it's immediately evident that James (Speedman) and Kristen (Tyler) are not a happy couple escaping on a weekend retreat. There's trouble in this little paradise and the pair's sadness is inextricably linked to the terror they're about to endure.

That terror arrives in the middle of the night, in the form of a masked woman who knocks on the front door, asks for someone who doesn't live there and then disappears. You probably won't be surprised to learn that she's not gone for good and she's not alone. (One of her compatriots is wearing a shapeless, flour-sack mask that may have been stolen from the prop department of "The Orphanage." And because masks are dehumanizing, and therefore creepy, the effect is almost as frightening here.)

As the masked trio make their presence (if not their purpose) known, they instigate a home-invasion nightmare of epic proportions. What can you do when you're being stalked in your own house by three lunatics? Not much, apparently. Everything that can go wrong for our heroes does (phone lines are cut, ditto the lights), but James and Kristen respond with admirable gumption, and, despite occasional lapses into Stupid Horror Movie Behavior, generally keep their wits about them. (Until, finally, they don't.)

Bertino can claim credit for several wise decisions: He kept the movie short (around 90 minutes); he didn't break the nearly unbearable tension until the final five minutes; and, perhaps most important, despite the movie's speedy pace, he allows the main characters time to develop personalities. As we've learned from umpteen lesser horror flicks, there's nothing less compelling than watching characters we don't care about (or who might as well be cardboard cutouts) getting chased around by ax-wielding loons. Real suspense requires a real connection, and Bertino -- with Tyler and Speedman -- has created both.